We can, from the instances above given, form a pretty good guess at the way in which the auxiliary or meaningless class of sounds came into use in any language. Each of these must once have had a distinct significance by itself, then (getting meanwhile a little changed in form probably) it gradually lost the separate meaning and became only a particle of speech, only an adjunct to other words. In another way, we may say that before man spoke of ‘on the rock’ or ‘under the rock’ he must have used some expression like ‘head of rock,’ or more literally ‘head rock’ and ‘foot rock;’ and that as time went on, new words coming into use for _head_ and _foot_, these earlier ones dropped down to be mere adjuncts, and men forgot that they had ever been anything else. Just so no ordinary Frenchman knows that his _oui_ and _il_ are both sprung from the same Latin _ille_; nor does the ordinary Englishman recognize that _ago_ is a past participle of ‘go;’ nor again, to take a new instance, does, perhaps, the ordinary German recognize that his _gewiss_, ‘certainly,’ is merely an abbreviation of the past participle _gewissen_, ‘known.’ * * * * * We have now followed the growth of language through [Sidenote: Root-sounds.] two of its stages, first, the coining of the principal or essential parts of speech, the nouns, adjectives, and verbs; and secondly, the coining at a later date of the auxiliary parts of speech, the prepositions, adverbs, and conjunctions, and (where they exist) the enclitics _the_ and _a_; these last, however, (_as separate words_,[21]) are wanting from a large number of languages. A third stage is the variation of certain words to form out of them other words which are nearly related in character to the first. We may speak of this process as a process of ringing the changes upon certain _root-sounds_ to form a series of words allied in sound and allied in sense also. We have several instances of such groups of allied words in our own language. _Fly_, _flee_, _flew_, _fled_, are words allied in sound and in sense. In these cases the sound of the letters f-l constitutes what we may call the root-sound. And it may be said at once that those languages are said to be related in each of which a certain number of words can be traced back to root-sounds which are common to the two or more tongues.